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(Apologies in advance for opening a topic again on something that's been discussed a lot but don't want to reopen old discussions either...) Apologies also if someone has already pointed out what follows... S = 1/2 a.t^2 The concensus in the forum seems to be that the best way (no atmosphere) to take off and the most efficient way to land is expend the greatest percentage of work on the horizontal velocity component to either establish or eliminate orbital speed. This is in line with Newton's idea that if he could climb a high enough mountain and shoot a baseball toward the horizon at a high enough (instantaneous) speed, it would come back to hit him in the head 90 minutes later. The problems with screaming in low and fast for a landing are terrain clearance; pilot reaction time (as this will effectively be a suicide burn which is what makes it efficient); and therefore inaccuracy. I just tried this at my mining camp on Moho and touched down softly 24m from the target. (For those who religiously don't use MechJeb, leave the autopilots alone but MechJeb provides essential displays; in this case: Orbit Info; Surface Info; Vessel Info and Rendezvous Info.) I suggest the procedure is as follows: perform any desired inclination change 270 degrees before the target; lower the periapsis to a few km above the target, 180 degrees before the target; on the first attempt, use the altitude of the highest mountain as your target periapsis to avoid premature contact; watch true altitude for a minimum which will tell you how much you can lower the target periapsis on future landings; your speed will increase as you get lower which means that your orbital speed will serve only as an initial (low) approximation; Vessel Info displays your max deceleration rate. Reducing speed from 828 m/sec with a deceleration of 16.18 m/sec/sec will take 51.2 secs; S = 1/2 a.t^2 suggests that in that 51.2 secs you will travel 21.2 kilometers; when the Rendezvous Info display says you are 21.2 km from the target (or a little before if you are nervous), fire Full Astern; Using a periapsis of 6km above the target, I arrived 2km over the target and a little after the target (because I got distracted and fired late). And vertical and horizontal speed zeroed out approximately together, which is what you'd expect from retrograde. (The MSA for this approach is actually around 5.1km, so I possibly can tune this down near 1.1 km above target.) You exit suicide burn at this time or a little earlier, when your confidence is ready. Then fly the navball in what is pretty close to a short vertical descent. The reputation is that this low, screaming approach is inaccurate, but if you are avoiding terrain anyway, it adds up to "landing" (arrival) a kilometer above the target and then a short walk in the park to get down and dusted off. The hard part is knowing when to fire and this is where the equation above is your friend. A quick manipulation of that equation gives you the following: S = 1/2 v^2/a S = 1/2 828*828/16.18 = 21.186 km (If there's enough interest, I'll make a video.)
I've built a prototype of a VTOL ion-drive "hover-raft" for lo-grav environments up to and including Duna. Gossamer Albatross 1.0 It's dual purpose is local tourism as well as commuter flights over about a 30-degree radius of the reference body's circumference. It could serve for rescue too. "Hover-raft" and "mono-prop commuter" are two nicknames for it. Unfortunately, I think I've reached the limits of my VAB capability with this project, so I'd like to open a competition. (Maybe something similar has been done before? Please let me know and provide a link and thank you!) Otherwise, I'd like to propose a challenge. Take a look at the craft file above. I want an 8-seater (6 or above). VTOL. Stays aloft on ion-power alone. Is only fueled with xenon and mono-prop. Is fun to fly and OK to require plenty of advance flight planning. You may use monoprop, e.g. OMS, to propel to speed or to initiate/augment ascent. It *must* be equipped with a refueling "spoon" (similar to that included in 1.0 above): a standard-size dock facing downwards for mating with a fuel-truck rover. Mono-prop is used for initial acceleration and final deceleration and the usual attitude adjustments. After that it should have at least 30 minutes duration aloft on ion-power. The v1.0 posted here needs weight reduction and I wanted to remove the stack bi-couplers and replace the retract landing gear with lighter-weight fixed gear. One last comment: "form follows function". I don't care how ugly the result is (check out my effort!!) as long as it is fun to fly and good for exploration, tourism and medium-distance commuting. Apologies to resorting to hoping other people would spend their own valuable time, energy and expertise working on this but I know that a) I am at the limit of what I can do with the VAB, and b ) there are rocket craftsmen out there who might revel in a challenge like this and enjoy producing something that I believe will be very useful and fun to a lot of others. Want to take a crack at it? Be my guest! Please post your work back in this topic and get some recognition/kudos for your ability!